1. The Field Of The Invention
The present invention relates to switching means for synchronizing a voltage-controlled oscillator output with a variable input Baud Rate Clock. More specifically, the present invention relates to automatic switching means for electronically switching a Baud rate counter ratio in response to a change in the input signal Baud rate.
2. The Prior Art
In a parallel-to-serial data multiplexing system, it is sometimes desirable that the serial output clock rate be an integer multiple of one of the input circuits. If a crystal oscillator is used, the system frequency is fixed, and the subdivisions of the system frequency which represent the sample frequency is likewise fixed. Furthermore, if the input Baud Rate Clock is variable, a lack of synchronization between the sampling frequency and the input Baud rate may occur, particularly at high Baud rates, which can cause intolerable variation, i.e., "jitter", in the output.
In order to adjust for such fluctuations at high Baud rates, a voltage-controlled oscillator using a Phase Locking Loop to lock its output frequency with the input frequency may be used so that a constant output to input ratio is maintained. The transmitted output is thereby free from jitter. Heretofore, however, no convenient scheme had been devised for adjusting the output frequency whenever the selected input Baud rate is to be changed. The industry, therefore, has been in need of a convenient switching scheme for automatically synchronizing a voltage-controlled oscillator output frequency with a variable input Baud Rate Clock.